Heat transfer enhancement of spray cooling in straight-grooved surfaces in the non-boiling regime

Experiments were performed on six straight-grooved surfaces and one flat surface placed horizontally using pressure atomized full-cone nozzles to study the effects of structure parameters of surfaces and volumetric fluxes on heat transfer during water spray cooling in non-boiling regime. In the experiments, the surface temperature was set below 100 °C, and the nozzle was fixed 1.0 cm above surfaces. The results show that the surface with the groove depth of 0.5 mm and the groove width of 0.4 mm has the largest heat flux enhancement at the volumetric flux of 1.604 L/(m2 s). While for the volumetric flux of 12.73 L/(m2 s), the optimal heat transfer surface is another surface with the groove depth of 0.5 mm and the groove width of 0.2 mm, the heat flux of which is 202.5 W/cm2 enhanced about 61.6% relative to the flat surface at the surface temperature of 80 °C. Three distinct heat transfers, which are heat transfer on top surface of fins, on sidewall of grooves and on bottom of grooves, are identified for spray cooling on straight-grooved surfaces. Based on the analysis of force acting on the falling droplet, it is found that the residual velocity of droplet is much larger for the volumetric flux of 12.73 L/(m2 s) than the volumetric flux of 1.604 L/(m2 s), which make the sidewall and bottom surface of grooves to be better cooled by spray at the volumetric flux of 12.73 L/(m2 s). That is why the optimal heat transfer enhanced surfaces are different for two volumetric fluxes. A heat transfer model is derived which can accurately predict the heat fluxes of straight-grooved surfaces at the volumetric flux over 12.73 L/(m2 s).